This application relates to U.S. application Ser. No. 08/559,283, filed Nov. 15, 1995, which is a continuation-in-part of U.S. application Ser. No. 08/364,479, filed Dec. 23, 1994, now U.S. Pat. No. 5,722,067.
This invention relates to a cellular telephone system that allows only pre-paid subscribers to complete cellular telephone calls and, in particular, to a fraud resistant, pre-paid subscriber system that does not require special hardware connections to existing telephone networks.
A cellular telephone is a multi-frequency, portable transceiver, typically constructed with state of the art integrated circuits and capable of transmitting voice and digital data reliably almost anywhere in the world. Except for cost, a cellular telephone would likely be the appliance of choice for every person in the country. A cellular telephone costs at least three times as much, per month, as a xe2x80x9cland line,xe2x80x9d i.e. as a telephone connected by wire to a public switching network. Despite the sophistication and quality of cellular telephones, the relatively high cost of a cellular telephone is not the telephone itself but the charges for the use of the telephone. Unfortunately, a significant portion of the cost of the system is due to theft of services and many techniques for detecting or thwarting theft have been proposed or implemented.
Some security systems rely on calling patterns to detect theft and such systems are prone to false positives, i.e. incorrectly identifying a legitimate call as an illegal call. Also, such systems require a number of calls to detect theft, which means that, if the calls were illegal, the cost of the calls must be absorbed by someone other than the caller. It is preferred to have a system that can detect theft of service as soon as the theft is attempted.
Another aspect of cost is the ability of a subscriber to pay for services compared to the subscriber""s desire to use the services. Many subscribers sign up on the basis that the cellular telephone will only be used for emergencies and then find themselves defining xe2x80x9cemergencyxe2x80x9d progressively more broadly. For many subscribers, it has been found beneficial to provide a pre-paid subscription that is self-limiting in the sense that the service is terminated when the payments are used up. U.S. Pat. No. 5,353,335 (D""Urso et al.) describes a modified network architecture in which a special platform for pre-paid calling service is connected to a node in a public, switched telephone network.
The above-identified, related application also describes a pre-paid, cellular system. The system disclosed in the application requires no modification to cellular telephones and, for outgoing calls, uses the automatic number identification (ANI) from each cellular telephone as a file link to identify and to authenticate the cellular telephone. Incoming calls are transferred to the mobile telephone switching office (MTSO) in which a number of lines are reserved for pre-paid subscribers. An incoming call is screened for a valid number and a positive, pre-paid balance by the subscription service and is then passed on to the subscriber. If the MTSO will not dedicate lines to pre-paid subscribers, a significant geographic area is unavailable to a specific but viable market.
A system requiring no modification to the cellular telephone is most easily implemented but the security of such a system is not as great as when the cellular telephone is modified. A problem with a system requiring modification to the cellular telephone is that physical access to the telephone is required.
In view of the foregoing, it is therefore an object of the invention to provide a cellular telephone system for pre-paid subscribers in which the system is transparent to existing telephone networks.
Another object of the invention is to provide a pre-paid subscription service that detects theft as it occurs and terminates the call.
A further object of the invention is to provide a pre-paid cellular telephone system that monitors both outgoing and incoming calls without the need for dedicated lines at an MTSO.
Another object of the invention is to provide a secure, pre-paid cellular telephone system requiring only software modification to existing cellular telephones to adapt the telephones to the system.
A further object of the invention is to provide a secure cellular telephone system in which modifications to a cellular telephone do not require physical access to the telephone.
The foregoing objects are achieved in this invention in which a pre-pay service unit uses pseudo-numbers to identify subscribers and substitutes actual numbers to complete a call after verification of authenticity and verification of a positive balance in the subscriber""s account. The service unit and the cellular telephone exchange data in the process of authentication. The pseudo-numbers are combined with other data to provide a secure check of the identity of the cellular telephone and the authenticity of the call. It has been found that modifying a cellular telephone to share identification between the system and the telephone increases the security of the system and enables the operation of the system to be transparent to an MTSO.
In particular, for outgoing calls, the cellular telephone first transmits an xe2x80x9c800xe2x80x9d number and the ANI. The xe2x80x9c800xe2x80x9d number is the telephone number of a pre-pay service unit which receives the call. A switching network in the service unit then requests the dialed number, which the cellular telephone transmits with a security code and status data. If the data is authentic, the dialed digits are then passed to a local exchange carrier to complete the call. For incoming calls, a pseudo-number directs the call to a pre-pay service unit, which converts the pseudo-number to the actual telephone number of a subscriber""s cellular telephone. After exchanging data with the subscriber""s telephone, and after verifying authenticity and credit balance, the call is completed. Both incoming and outgoing calls can be monitored for charges and a call is terminated if a subscriber""s balance reaches zero.